Method of heating and apparatus therefor



Dgc. 10, 1940. V w. B. MATHEWS 2224,8137

METHOD OF HEATING AND APPARATUS THEREFOR Filed May 20, 1957 W FIGJ.

\NVENTCR WALLACE B. MATHEWS eg [7 LM ATTORN EY Patented Dec. 10, 1940 PATENT OFFICE METHOD OF HEATING AND APPARATUS THEREFOR Wallace B. Mathews, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application May 20, 1937, Serial No. 143,745

12 Claims.

Thisinvention relates to an apparatus and method for heating fluids and refers especially to such apparatus and method wherein hydrocarbon liquids and gases are heated to conversion temperatures by being passed through a plurality of tubes which are positioned adjacent boundary surfaces of a combustion chamber and adapted to be heated predominantly by radiant heat. More particularly, the invention refers to a furnace which is provided with an elongated combustion chamber divided into a plurality of separate communicating combustion sections having a separate coil in each combustion section, and to a method of heating a plurality of separate streams of hydrocarbon fluids therein. The invention has general application, however, in providing any combustion chamber with relatively short tubes arranged in a plurality of rows along an elongated boundary surface of the chamber.

Among the objects of the invention is to provide a generally new and improved structure for a furnace of the type above indicated; to provide in such structure a new and improved means for supporting and interconnecting the tubes, particularly at the ends thereof which are'distant from the end walls of the combustion chamber; to provide a structure and arrangement in such furnaces which permits all headers and the like connected to the ends of the various tubes to be insulated from the interior of the combustion chamber and from the outside atmosphere; to provide a structure and arrangement of parts which generally assist in causing the tubespositioned within separate combustion sections of an elongated combustion chamber to be heated substantially entirely by radiant heat; and to provide a new and improved arrangement for the burners or the like in such furnaces.

It is a further object of the invention to provide such furnaces with a plurality of separate convection sections and to regulate the amount and distribution of heat within each of the combustion and convection sections by selectively controlling the quantity and flow of hot products of combustion within the furnace.

It is also an object of the invention to provide a new and improved method of heating a plurality of separate streams of hydrocarbon fluids within a single furnace setting and for controlling the amount and distribution of heat supplied to each of the separate streams.

Other objects and advantages reside in the structure, arrangement and combination of parts hereinafter described and illustrated in the accompanying drawing in which like reference characters are used to designate like parts in the several views, and in which:

Fig. 1 is a plan view partly in section of a furnace constructed in accordance with the invention; 5

Fig. 2 is a sectional elevation of a portion of the furnace taken along the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary sectional plan view illustrating a modification of the furnace shown in Fig. 1.

Referring to the drawing and to Figs. 1 and 2 in particular, the numeral I refers in general to a furnace which is particularly adapted for the pyrolytic conversion of hydrocarbon fluids. Only a portion of the furnace is shown in section in Fig. 1, it being understood that the structure and arrangement of parts at both ends thereof are similar. The furnace comprises an elongated substantially rectangular combustion, chamber 2 and a convection section 3 at each end of the combustion chamber. The convection sections are provided with ducts or the like 4 at the bottom thereof for conveying hot products of combustion to a flue or other apparatus, and are separated from the combustion chamber by means of bridge walls 5 which form a part of the end walls for the combustion chamber. The bridge walls 5 extend upwardly from the bottom of the furnace and provide a space at the upper portion thereof for the passage of hot products of combustion from the combustion chamber into the respective convection sections.

Tubes 6 are arranged in the convection sections in any desired or conventional manner, andare adapted to be swept by hot gases passing through such sections. The tubes 6 extend through the end walls of the convection sections inthe conventional manner and are provided with headers or other fittings I which interconnect the tubes in the desired sequence. The fittings 1 may be enclosed by insulated housings 8 which may be provided with doors suitably hinged to the remainder of the housing, as indicated at 9, to per mit ready access to the fittings and the ends of the tubes 6 for the purpose of cleaning or removing the same. ,The, fittings I may be provided with the usual cleaning plugs.

When a convection section is arranged atone or both ends of the combustionchamber, as illustrated in the drawing and hereinabove described, the ends walls of the convection section may be set back sufficiently from the front and rear walls [0 and II, respectively, of the combustion chamber to permit the fittings 1 and, optionally, housings 8 enclosing the same, to lie inside of the reentrant recesses which are provided at each corner of the combustion chamber for a purpose to be hereinafter described. The invention contemplates, however, that one or more convection sections may be arranged in any desired manner with respect to the combustion chamber, such, for example, as to the side or on top of such chamber, or the convection sections may be omitted.

The elongated vertical front and rear walls In and II, respectively, of the combustion chamber are provided each with a reentrant portion I2 at a central portion of the combustion chamber. The reentrant portions I2 serve to divide the combustion chamber into two separate but communicating combustion sections. The combustion chamber 2 is also provided with reentrant portions I at each corner thereof. Horizontal tubes I3 are arranged along the front and rear walls on each side of the reentrant portions I2, and horizontal tubes I4 are arranged along the bridge and end wall 5 at each end of the combustion chamber. The side walls I6 of the reentrant portions I2 and the respective side walls of the reentrant portions I5 extend into the combustion chamber a distance sufiicient to permit the respective ends of the tubes I3 and I4 to extend through such walls into the recesses provided exteriorly of the combustion chamber by the respective reentrant portions I2 and 15. The respective ends of the tubes I3 and I4 are interconnected in any desired sequence by fittings which are positioned within such recesses formed by the reentrant portions I2 and I5 of the furnace, as indicated at I! and I8. The ends of the tubes and the fittings interconnecting the same in the recesses provided by reentrant portions l2 may be protected from the atmosphere by insulated doors or the like I9 which may be hinged to the furnace walls, as indicated at 251, to permit ready access to the fittings and ends of tubes. In a similar manner the ends of the tubes and fittings positioned within the recesses provided by reentrant portions It may be protected by means of insulated housings 2I. The sides of the housings 2| may be hinged, as indicated at 22. The fittings I1 and I8 may be provided with the usual cleaning plugs.

The wall tubes I3 and I4 are so positioned as to be substantially outside of the path of hot products of combustion sweeping through the combustion chamber and are heated predominantly by radiant heat. The reentrant portions I2 and I5 assist in this respect by providing interior recesses along the side walls I I3 and II which permit the side wall tubes I3 to be set back out of substantial direct contact with the hot products of combustion contained in the longitudinal central portion of the combustion chamber. At the same time the inside walls of the reentrant portions tend to maintain such combustion products in the central portion of the combustion chamber, particularly when the opening from the combustion chamber into a convection section or other exit means for hot gases is located in a portion of the boundary surface of the combustion chamber which does not include a portion of such surface which defines said interior recesses. Thus, in the furnace illustrated in the drawing the openings from the combustion chamber to the convection sections are positioned between the walls of the respective corner reentrant portions and do not extend into any walls defining the interior recesses within which the tubes I3 are positioned. In

this manner the hot combustion products are withdrawn from only the longitudinal central portion of the chamber, and tubes I3 are set back substantially out of the path of such products. The reentrant portions I2 also permit the wall tubes I3 to be of relatively short length and arranged in a plurality of rows. At the same time such portions provide exterior recesses insulated from the interior of the combustion chamber and from the outside atmosphere for the ends of the tubes I3 and the connections thereto. The reentrant portions I5 provide similar exterior recesses at the ends of the combustion chamber. As illustrated in the drawing, the respective tubes I3 and I4 are arranged in the form of two separate three-sided coils positioned in the respective combustion sections provided in each end of the combustion chamber 2 by the reentrant portions I2. Thus, the adjacent ends of the respective tubes I3 and IQ are illustrated as being interconnected by the 90 corner fittings I8 while the opposite ends of the respective tubes I3 are illustrated as being interconnected by the 180 return bends I'I. With this arrangement two separate streams of oil or the like may be introduced into two of the lowermost tubes I3 at the ends thereof positioned within one of the recesses formed by the reentrant portions I 2 and thence passed successively through the three lowermost tubes positioned in the respective combustion sections at each end of the combustion chamber 2. The two separate streams are then passed upward into the next row of tubes i3 and I4 and thence through the successively higher rows of tubes until one stream has traversed all of the tubes located in one of said sections and the other stream has traversed all of the tubes located in the other section. The furnace illustrated in the drawing is particularly adapted for such two-coil arrangement, but it is to be understood that the invention contemplates any desired arrangement and interconnections for the various wall tubes I3 and I4. The oil or the like may be passed through the tubes 6 located in the respective convection sections of the furnace either before, after or both before and after its passage through the combustion section.

The flow lines shown on Fig. 2 illustrate an example of two flows which may be advantageously employed in a two-coil furnace of the type described. In this arrangement of the tubes the stream of oil which is passed through the righthand side of the furnace, as shown in the drawing, is first passed through the lower portion of the convection section in a direction countercurrent to the hot gases flowing through such section. Thence'it is passed upwardly through the coil in the right-hand radiant heating section and thence through a coil in the upper portion of the convection section in a direction concurrent with the hot gases flowing therethrough. The stream of oil which is heated in the other portion of the furnace (not shown but similar in arrangement to the right-hand side) is passed upwardly through a coil positioned in the convection section and is thence passed upwardly through the coil positioned in the left-hand radiant section. It is to be further understood, however, that the invention contemplates any desired interconnections between tubes in the convection section and tubes in the combustion section for any desired flow of oil or gas therethrough and is not limited to the particular examples of the flow thus illustrated and described. The combustion section may also be provided with a plurality of floor tubes androof tubes (not shown) V and the streams of oil passed therethrough in any desired sequence.

Suitable means such as the burners 23 are provided in each of the combustion sections forintroducing hot products of combustion into the combustion chamber. The burners 23 are shown as extending through ports 24 positioned in the front and rear walls lfland I I of the combustion chamber. These ports are positioned to give the desired heat distribution within the respective combustion sections.

Since the'respective combustion sections are in communication with each other hot products of combustion from. one. section may be caused to flow through they convection section communieating with the other combustion section by pro- 'viding dampersor the like in the respective flues leading from the convection sections. When the convection sections communicate with. the respective combustion sections at non adjacent ends of the combustion sections, as illustrated in the drawing, the hot products of combustion from one combustion section may also be caused to pass through the other combustion section. To accomplish such distribution and flow of, the combustion products dampers 25 are shown positioned in the flues 4 vin Fig. 2 of the drawing. These dampers may be manually or automatically controlled and may be operated independently or as a unit. In this manner hot products of combustion from one combustion section may be utilized-to increase and control the radiant heat and the convection heatin the other combustion section and the convection section commun cating therewith. At the same portions serve to separate the combustion sections and thereby permit a substantial temperature differential to be maintained in the various combustion. sections. The. reentrant portions also shield the tubes in one combustion section from the. radiant heat in an adjoining combustion section.

It is thus rate streams of hydrocarbon fluids under entirely different temperature conditions radiant and convection heating sections of a single furnace, and to control such heating by separately regulating the quantity of hot products of combustion introduced into the various combustion sections by the burners 23 and by varying the portion of such products passed from one combustion section into another combustion section and the convection section associated therewith. In this manner the furnace may be used to heat a plurality of fluids requiring different amounts of heat, such, for example, as in the cracking'of gas oil inone section and the reforming of naphtha in another, and has greater flexibility both as to the temperature control for given stocks and as to the use of one or more portions or sections of the furnace for the heating of difierent stocks requiring difierent temperature conditions.

If the respective separate convection sections communicate with their respective combustion sections adjacent the reentrant portions 12 of the furnace and hence at the adjacent ends of the combustion sections the portion of hot products of combustion passed into each of the convection sections may be varied without causing products from one combustion section to pass through another combustion section. Such anarrangement may be desirable where it is desired to vary only time the reentrant possible to heat a plurality of sepain both the ucts froma' plurality of combustion sections.

-When one-or more convection sections are positioned to the side or on top of the corjnbustion chamber instead of at the endsthereof the burners may be positioned in the end walls of the combustion chamberjso as to directthe flame and productsof combustionlongitudinallyof the chamber. In this manner thepossibility of any flame impingement upon the tubes I3 is avoided. InFig'. 3 is shown a modified arrangement for the central reentrant portions" of" the elongated vertical front and rear walls of the combustion chamber. In this arrangement the right angular side walls l6" of the respective reentrant portions l2 are extended'i ito the combustion chamber a distance suflicient to provide a bay wherein burners or the like 2'3'" may be positioned. These burners extend'through 'theresp'ective walls l6 and are directed in the general direction of the respectiveend walls 5 of; the combustion chamber whereby the flames and hot products of combustion are directed"lorigitudinally of the combustion sections. l g

In the preferred embodiment of "this arrangement, however, those portions of the'walls 16% in which the burners are positioned are turned towards each other at an angle to the respective front and rear walls ['0' and I I,"as indicated in Fig. 3. In this manner the burners positioned. within one of the "reentrant portions l2: are turned somewhat towards corresponding burners positionedinthe other reentrantportion l2, and each of the burners 23 is directed in the general direction of a vertical corner of the combustion section which is "diagonally -opposite to the burner. The flames and hot products of combustionf'from' thegthusflflopposed burners collide within the respective"cornbustion' sections and create a desired degree'oftur-bulence within such sections. Such collisionat the sametime tends to'direct' the respective streams of combustion products longitudinally of the combustion section and prevents direct flame impingement upon the wall tubes l3. A similar result may be obtained by arrangingthe'burnersfor the like, 23' in a curved wall joining the respective ends'of the right angular side walls l6"of'each reentrant portion or by tilting the burners in such right angular side walls. Insulated shields 26 provided with hinged portions 21 may be provided in this modiflcatio-n'to protectlthe fltting's' ll from the atmosphere while permitting access of air to the burners 23' V 1' Additional burners, or the like, 23 maybe used with the arrangement of Fig. 3 and positioned in the end" and side walls of the respective combustion sections, as described in connection with Figs. 1 and 2. V In the furnace illustrated in Figs. 1 and 2 of the drawing the reentrant'portions 12 are positioned midway between the'ends of the furnace whereby the furnace is symmetrical with respect to such portions. The invention contemplates, however, the provision of such reentrant portions at any point intermediate the ends of the elongated vertical walls or other elongated boundary surface or at a plurality of 'points' along the length of such walls and surfaces. It is thus apparent that the respective combustion sections" may be of dift'erent lengthsand that the furnace may be unsymmetrical with respect to one or'more reentrant portions similar tothe portions I2 or I2 in the drawing.

Many other modifications and variations'may be made'without departing from the spirit and scope of the invention, and only such limitations should be imposed as are included in the appended claims.

It is claimed:

1. In a heating apparatus for hydrocarbonfluids, a housing providing an elongated combustion chamber of substantially rectangular horizontal cross section, said chamber having a pair of end walls and an elongated vertical side wall, a reentrant bay in said side wall intermediate its ends, banks of horizontally positioned tubes arranged along the interior face of said wall on each side of said reentrant bay, one end of each of the tubes of said banks extending through the wall of said bay and terminating in the recess formed exteriorially of the combustion chamber by such bay, connections positioned within said recess for connecting the ends of the tubes of one bank to form one coil and connections positioned within said recess for connecting the ends of tubes of another bank to form another separate coil whereby a separate stream may be heated in said combustion chamber on each side of said reentrant bay;

2. In a heating apparatus for hydrocarbon fluids, a housing providing an elongated combustion chamber of substantially rectangular horizontal cross section, said chamber having a ,pair ofend walls and an elongated vertical side wall, a reentrant bay in said side wall intermediate its ends, banks of substantially horizontal tubes arranged along the interior face of said wall on each side of said reentrant bay, one end of each of said tubes extending through the wall of said bay and terminating in the recess formed exteriorly of'the combustion chamber by such bay, connections positioned within said recess for connecting the ends of the tubes of one bank to form one coil and connections positioned within said recess for connecting ends of tubes of another bank to form another separate coil whereby a plurality of streams may be heated in said combustion chamber, and a plurality of means extending through the wall of a reentrant bay and generally directed towards the end walls of the combustion chamber for introducing hot products of combustion into the interior of said chamber.

3. In a heating apparatus for hydrocarbon fluids, a housing providing an elongated combustion chamber of substantially rectangular horizontal cross section, a pair of opposite elongated vertical side walls defining lateral boundaries of said chamber, a reentrant bay correspondingly located in each of said side walls intermediate its ends, said bays serving to divide the combustion chamber into two communicating combustion sections, exit means for combustion gases disposed at each end of said elongated combustion chamber, banks of substantially horizontal tubes positioned within each of said combustion sections adjacent each of said vertical side walls, one end of each of said tubes extending through the respective walls of the reentrant bays and terminating within the recesses formed exteriorly of the combustion chamber by such bays, connections positioned within said recesses for said ends of the tubes, and in each reentrant bay a plurality of burner means extending through the wall thereof and generally directed towards the diagonally opposite corners of said combustion sections for introducing hot products of combustion into the interior of the combustion sections, whereby the flames and hot products of combustion from said burner means collide within the respective combustion sections and then pass longitudinally of the respective combustion sections thence to said exit means.

, 4. In a heating apparatus for hydrocarbon fluids, a housing providing an elongated combustion chamber of substantially rectangular horizontal cross section, a pair of end walls and opposite elongated vertical side walls defining the lateral boundaries of said chamber, a reentrant portion correspondingly located in each of said side walls intermediate its ends to subdivide said combustion chamber into communicating combustion sections, additional reentrant portions at each vertical corner of the combustion chamber, said intermediate reentrant portions and said corner reentrant portions forming recesses within the combustion chamber along eachv of said side walls on each side of the intermediate reentrant portion, banks of substantially horizontal tubes positioned along the interior faces of the side walls within said interior recesses on each side of said intermediate reentrant portion, the ends of said tubes extending through the respective walls .of said reentrant portions and terminating within the recesses formed exteriorly of the combustion chamber by such portions, connections positionedwithin said exterior recesses last mentioned for connecting the ends of said tubesrin respective banks to form a separate coil for each combustion section, means for introducing hot products of combustion into the interior of each combustion section, and exit means for said combustion products adjacent opposite ends ofsaid combustion chamber, whereby said tubes are positioned substantially out of the path of hot products of combustion within the combustion chamber and are heated predominantly by radiant heat.

5. In a furnace for heating a plurality of separate-streams of hydrocarbon fluids, a housing providing an elongated combustion chamber of substantially rectangular horizontal cross section, a pair of opposite elongated vertical side walls and a pair of end walls defining the lateral boundaries of said chamber, a reentrant portion correspondingly located in each of said side walls intermediate its ends, said intermediate reentrant portions serving to divide the combustion chamber into two communicating combustion sections, additional reentrant portions at each vertical corner of the combustion chamber, a coil positioned within each of said combustion sections, said coils comprising banks of substantially horizontal tubes positioned adjacent the interior faces of the side walls on each side of said intermediate reentrant portion and adjacent the interior faces of said end walls, the ends of said tubes extending through the respective walls of said reentrant portions and terminating within the recesses formed exteriorly of the furnace by such portions, corner fittings positioned within the said recesses provided by the corner reentrant portions for connecting together the adjacent ends of the respective side and end wall tubes, and return bend fittings positioned within said recesses provided by the intermediate reentrant portions for connecting together the respective opposite ends of the side wall tubes.

6. The method of heating separate continuous streams of hydrocarbon fluids in a heating apparatus provided with a chamber divided into a plurality of separate communicating combustion sections and having a plurality of separate convection sections communicating with the interior of said chamber whereby each of a plurality of said separate combustion sections communicates with a separate convection section, which comprises directly introducing hot products of combustion into a plurality of said separate combustion sections, distributing a portion of the total hot products of combustion from the plurality of combustion sections to each of said separate convection sections, passing a separate stream of hydrocarbon fluid through each combustion section, passing a plurality of said streams through separate convection sections, heating said streams predominantly by radiant heat from the hot products of combustion in the combustion sections and predominantly by indirect contactwith such products in the convection sections, and separately regulating the quantity of hot products of combustion introduced into the separate combustion sections by diverting some hot products of combustion from one combustion section to another combustion section and then passing them through a single convection section to impart diiierent amounts of heat to the separate streams in both the combustion and convection heating sections.

'7. The method of heating separate continuous streams of hydrocarbon fluids in a heating apparatus provided with a chamber divided into a pair of separate communicating combustion sections and having a pair of separate convection sections communicating with the interior of said chamber at opposite ends thereof whereby each of said separate combustion sections communicates with a separate convection section adjacent an end of the combustion section, which comprises directly introducing hot products of combustion into each of said separate combustion sections, distributing a portion of the total hot products of combustion from the combustion sections to each of said separate convection sections, passing a separate stream of hydrocarbon fluid through each combustion section, passing a plurality of said streams through separate convection sections, heating said streams predominantly by radiant heat from the hot products of combustion in the combustion sections and predominantly by indirect contact with such products in the convection sections, and separately regulating the quantity of hot products of combustion introduced into the separate combustion sections by diverting some hot products of combustion from one combustion section to another combustion section and then passing them through a single convection section to impart different amounts of heat to the separate streams in both the combustion and convection heating sections.

8. The method of heating a plurality of separate continuous streams of hydrocarbon fluids in a heating apparatus provided with a chamber divided into a plurality of separate communicating combustion zones and having a pair of separate convection heating zones communicating with the interior of said chamber adjacent opposite ends of a pair of adjoining combustion zones, which comprises directly introducing hot products of combustion into said pair of separate combustion zones, distributing a portion of the total hot products of combustion from the plurality of combustion zones to each of said pair of separate convection heating zones whereby a portion of the hot products of combustion from one of said pair of combustion zones passes through the adjoining combustion zone, passing a separate stream of hydrocarbon fluid through each of said pair of combustion zones and the convection heating z'one communicating therewith, heating said streams predominantly by radiant heat from the hot products of combustion in the combustion zones and predominantly by indirect contact with such products in the convection heating zones, and separately regulating the quantity of hot products of combustion intro- .duced into the separate combustion zones and varying said portion of the total hot products of combustion distributed to each of the separate convection heating zones to efiect a different heating of the separate streams in said pair of combustion and convection zones.

9. A heating apparatus including a housing provided with an elongated combustion chamber substantially rectangular in horizontal cross section and including end walls and elongated side walls, a reentrant bay located in each of said side walls intermediate its ends, said bays serving to divide said combustion chamber intoa plurality of separate communicating combustion sections, banks of tubes arranged in said combustion sections on each side of said reentrant bays, said tubes in each combustion section extending into the recesses formed by said reentrant bays, means interconnecting the ends of tubes in said recesses of respective banks to form a separate coil for each combustion section, the tubes adjacent one sidewall of the combustion sections being substantially in the same vertical plane, means whereby hot products of combustion are introduced into each of said combustion sections whereby said coils are heated predominantly by radiant heat from said products of combustion, separate exit means for each of said combustion sections, and means associated with each oi said exit means for controlling the quantity of products of combustion passing through said exit its ends, said bays serving to divide said combustion chamber into two separate communicating combustion sections, a convection section associated with each of said combustion sections, a plurality of horizontally arranged tubes positioned within each of said combustion sections adjacent said vertical side walls, one end of each of said tubes extending through the respective walls of said reentrant bays and terminating within the recesses formed exteriorly of said combustion chamber by said bays, means within said recesses for connecting the ends of tubes in respective combustion sections to provide a separate coil for each combustion section, a plurality of tubes in each of said convection sections, means whereby hot products of combustion are introduced into each of said combustion sections whereby said tubes in said combustion sections are heated predominantly by radiant heat, separate exit means associated with each of said convection sections, and means associated with each of said exit means for controlling the quantity of products of combustion passing from said combustion sections through said convection sections and over said tubes in said convection sections and through said exit means whereby a portion of the hot products of combustion from one combustion section may be added to the hot products of combustion in another combustion section to maintain said last mentioned combustion section at a higher temperature than the first mentioned combustion section.

11. A heating apparatus including a housing provided with an elongated combustion chamber substantially rectangular in horizontal cross section and having end walls and elongated side walls, a reentrant bay located in each of said side walls intermediate its ends, said bays serving to divide said combustion chamber into two separate communicating combustion sections, a plurality of horizontally arranged tubes positioned within each of said combustion sections adjacent said vertical side walls and end walls, one end of each of said tubes extending through the respective walls of said reentrant bays and terminating within the recesses formed exteriorly of said combustion chamber by said bays, additional reentrant portions at the ends of said combustion chamber forming recesses for receiving the other ends of said tubes and the ends of said end wall tubes so that relatively short tubes may be used which are easily removable, means within said reentrant bay recesses and reentrant portion recesses for connecting the ends of side wall tubes in one combustion section to each other and to said end wall tubes to provide a separate coil for each combustion section, the tubes adjacent one side wall of adjacent combustion sections being in substantially the same plane, means whereby hot products of combustion are introduced into each of said combustion sections whereby said tubes in said combustion sections are heated predominantly by radiant heat, separate exit means associated with each of said combustion sections and means associated with each of said exit means for controlling the quantity of products of combustion passing from said combustion sections and through said exit means whereby hot products of combustion from one combustion section may be added to the hot products of combustion in another combustion section to maintain said last mentioned combustion section at a higher temperature than the first mentioned combustion section.

12. The method of heating separate continuous streams of hydrocarbon fluids in a heating apparatus comprising a chamber provided with a pair of combustion sections and a pair of convection sections each adapted to receive hot products of combustion from both of said combustion sections, which comprises directly introducing hot products of combustion into each of said pair of combustion sections, distributing substantially all of said products of combustion from one of said combustion sections and a part thereof from the other combustion section to one of the convection sections and the other part of said products of combustion from the last mentioned combustion section to the other of said convection sections, passing a separate stream of hydrocarbon fluid through each combustion section and a different one of said convection sections, and heating said streams predominantly by radiant heat from said hot products of combustion in the combustion sections and predominantly by convection heat from such products in the convection sections.

WALLACE 1B. MATHEWS. 

